1. Field of the Invention
The present invention relates to a liquid discharging head for discharging desired liquid by bubble generation induced by application of thermal energy to liquid, and a liquid discharging apparatus and a printing system utilizing such liquid discharging head, and more particularly to a liquid discharging head having a movable member which is displaced by bubble generation, and a liquid discharging apparatus utilizing such liquid discharging head.
The present invention is applicable to various apparatus such as a printer for effecting recording on various printing media such as paper, yarn, fiber, fabrics, leather, metal, plastics, glass, timber or ceramics, a copying machine, a facsimile apparatus provided with a communication system, or a word processor having a printer unit, and to an industrial recording apparatus integrally combined with various processing apparatus. "Printing" used in the present invention means not only provision of an image having meaning such as a character or a graphic to the printing medium but also provision of a meaningless image such as a pattern to the printing medium.
2. Related Background Art
There is already known an ink jet printing method, so-called bubble jet printing method, which achieves image formation by providing ink with energy such as heat to induce a state change in the ink, involving a rapid volume change (generation of a bubble), for discharging ink from a discharge port by the action force based on such state change, and for depositing thus discharged ink onto a printing medium. In the printing apparatus utilizing such bubble jet printing method, there are generally provided, as disclosed for example in the U.S. Pat. No. 4,723,129, a discharge port for ink discharge, an ink path communicating with the discharge port, and a heat generating member (electrothermal converting member) provided in the ink path and constituting energy generating means for generating energy for discharging the ink.
Such printing method provides various advantages such as printing an image of high quality at a high speed with a low noise level, and easily obtaining a printed image of a high resolution, including a color image, with a compact apparatus, since, in the printing head utilizing such printing method, ink discharge ports can be arranged at a high density. For this reason, such bubble jet printing method is being recently utilized not only in various office equipment such as printers, copying machines and facsimile apparatus but also in industrial systems such as textile printing apparatus.
With such spreading of the bubble jet printing technology into the products of various fields, there have emerged various requirements to be explained in the following.
For example, for a requirement for improving the efficiency of energy, there is conceived optimization of the heat generating member, such as the adjustment of the thickness of the protective film. This technology is effective in improving the efficiency of propagation of the generated heat to the liquid.
Also for obtaining the image of higher quality, there have been proposed a driving condition for satisfactory liquid discharge, realizing a higher ink discharge speed and stable bubble generation, and an improved shape of the liquid path for realizing a liquid discharge head with a high refilling speed of the discharged liquid into the liquid path.
Among such liquid path shapes, a Liquid path structure shown in FIGS. 34A and 34B is disclosed for example in the Japanese Patent Laid-open Application No. 63-199972. The liquid path structure and the head manufacturing method disclosed in the above-mentioned patent application are based on an invention utilizing a backward wave (pressure directed opposite to the discharge port, namely toward a liquid chamber 12), resulting from the bubble generation.
The invention shown in FIGS. 34A and 34B discloses a valve 10, which is positioned separate from the generation area of the bubble generated by a heat generating element 2 and opposite to the discharge port 11 with respect to the heat generating element 2.
In FIG. 34B, the valve 10 is so disclosed, by a manufacturing method utilizing for example a plate member, as to have an initial position sticking to the ceiling of the liquid path 3 and to hang down into the liquid path 3 with the generation of a bubble. This invention is disclosed to suppress the energy loss by controlling a part of the above-mentioned backward wave by the valve 10.
However, in such structure, the suppression of a part of the backward wave by the valve 10 is not practical for the liquid discharge, as will be made apparent by the consideration of bubble generation in the liquid path 3 containing the liquid to be discharged.
On the other hand, the present inventors already filed a patent application on a line-type liquid discharge head in which discharge ports and electrothermal converting members are arrayed approximately corresponding to the width of the printing medium, and a liquid discharge apparatus utilizing such liquid discharge head. The liquid discharge head disclosed in this patent application is formed by precisely arranging plural heater boards, each having plural electrothermal converting members, on a base plate, and thereon adjoining a cover plate provided at an end thereof with plural ink discharge ports and with plural grooves respectively communicating with the discharge ports and extending from the end to the other end, toward the plural electrothermal converting members so as to close such grooves.
In the liquid discharge head containing an array of the plural heater boards as disclosed by the present inventors, the bubble generating power may leak at the junction of the neighboring heater boards if the cover plate is misaligned in the direction of array of nozzles and a nozzle is positioned at such junction. In such nozzle with leaked bubble generating power, the amount of discharge is reduced to generate a white streak in the printed image, thus deteriorating the image quality thereof.
Also such line-type liquid discharge head may result in fluctuation of the discharge amount, causing unevenness in the image, due to the influence of rear crosstalk, for example depending on the order of driving, and there has been desired a satisfactory printing without defective discharge or without unevenness.